The present invention relates to the production of semiconductor chips and other devices by photolithography. In particular it relates to creating devices with unique codings or other unique visual, optical or electronic properties. In a different sense the invention relates to the device itself and the design process of the device. Yet other aspects of the invention are the creation of tamper-proof implements that carry an electronic signature or cryptographic key. The invention also relates to reliability tracking of electronic devices and systems. Finally, an important aspect of the invention is related to reconfiguring devices containing several design versions or redundance functional units, such as for parametric experiments on an analog chip.
Modern production of semiconductor chips and also of surface acoustic devices, thin-film magnetic heads and similar devices is done by steppers. Modern steppers use four times reduction, excimer lasers as illumination source and use a step-and-scan principle where the wafer and reticle are scanned during exposure. In this context any type of stepper will be referred to as a stepper or as a scanning stepper where the distinction is important.
The important property of a stepper is that it produces identical copies of the same die by exposing the same mask at each exposure site. By doing so in an efficient way it provides high through-put and production economy. There are situation and cases where the chips should not be identical, such as for parameter try-out in research and development (RandD). The manufacturer is then forced to complicated procedures, like writing part of the pattern in an e-beam pattern generator or performing focussed ion-beam modification of the devices.
In other cases there is a need to provide a unique signature or code or programming to each chip. A common way to include such codes is by using electronically programmable circuits, often by changing reversibly or irreversibly the potential of a floating gate electrode, or by programmable fused links or so called anti-fuse links. In either case there are extra process steps, extra manufacturing cost and/or extra driving involved.
It is therefore an object of the present invention to provide a method and an apparatus to alleviate said shortcomings in the prior art.
This object is achieved with the invention according to the appended claims.
The invention devices a method to do such unique programming in a standard process with very little extra cost incurred. The invention allows virtually every ship to have a visually or electronically readable unique code. The code can be used as a serial number for a processor, for self configuration in networked devices or for tracking of faults and errors back to the lot, wafer and chip during manufacturing, thereby providing data for quality improvement.
Another aspect of the invention is that it provides a design block that can be included in any standard design to provide a visually or electronically readable code or a chip-unique programming. The block can provide a combination of a layout block and a computer program or compilation of data that together provides the desired programming at the time of exposure. The invention devices a method by which the code generation can be specified at design time and executed in an automated fashion.
The words coding, programming and personalization are used interchangeably throughout the application to denote the creation of a function that is different between different dies or chips. The apparatus or attachment that writes the code or programming is called a code-writer.